This PLOS article presents findings from a qualitative investigation of ethical and participatory issues related to the conduct of HIV prevention trials among marginalised populations in Thailand. This is a context where several previous large-scale biomedical HIV prevention trials had had to close prematurely. It was evident that there were difficulties in working and communicating with marginalised groups with different cultural and language backgrounds.

Findings suggested ways to improve ethical and participatory practice. These emphasised many of the aims and skills of community engagement practitioners (conducting strong informed consent processes, good communication across language and literacy differences and a recognition of participant rights).

Key informants felt that communication was the basis of ethical understanding and trust within a trial contexts, and important for a trial participants’ ability to exercise free will. They also suggested that efforts to improve practice would result in better relationships between research stakeholders and research investigative teams and by extension, better, more ethical participatory trials.